Screen structure for color image-producing cathode ray tubes of the index type



June 2, 1964 J CHATTEN 3,135,891

SCREEN STRUCTURE FOR COLOR IMAGE-PRODUCING CATHODE RAY TUBES OF THEINDEX TYPE Filed June 23, 1960 INVENTOR. .m/m 8. (l/A77! United StatesPatent 3 135 $91 SCREEN STRUCTURE, FoR coLoR IMAGE-rigo- DUCING CATHODERAY TUBES OF THE INDaX This invention relates to screen structures forcolor image-producing cathode ray tubes of the index type, wherein thecolor image is produced by successive and repetitive electron beamscanning of elements emissive of light of different primary colors, suchas red, green and blue, and wherein an index signal is also producedwhich is utilized to effect coordination between instantaneous beammodulation and beam position, such coordination being essential forproper color rendition. Such cathode ray tubes are now well known. Theyare useful, for example, in color television receivers.

The screen structure of a tube of this type preferably comprisesphosphor stripes in successive triplets which extend transversely to thedirection of line scanning motion of the electron beam, the stripes ofeach triplet being successively emissive of light of different primarycolors, e.g. red, green and blue, as the beam traverses them. Thescanning of each color triplet represents one color cycle. The colorwriting frequency is the nominal rate at which the writing beamtraverses the color triplets, i.e. the numher of triplets traversed persecond. By way of example, this frequency may be 6 mo.

The index signal is produced by electron beam impingement of indexelements which may also be in the form of stripes extending transverselyto the direction of line scanning. They may be composed of a fluorescentmaterial, such as zinc oxide, having a spectral output in thenon-visible light region, and the index signal may be derived from asuitable photo-electric cell arranged, for example, in a sidewallportion of the cathode ray tube out of the path of the electron beam andfacing the screen structure. Alternatively, the index signal may beproduced by secondary electron emission as well understood in the art.

In the manufacture of screen structures of the index type, the coloredlight-emissive elements and the index elements are preferably depositedby the photo-deposition method as known in the art, any other suitablemethod.

In a desirable form of such screen structure, the colored light-emissivestripes are deposited on a transparent substrate which may be thefaceplate of the cathode ray tube, and an electron-permeablelight-reflecting layer, preferably formed of aluminum, is applied tosaid stripes. The index stripes are deposited on said layer. This typeof screen structure is also well known.

In an improved form of such structure, as disclosed and claimed inPatent No. 2,842,697, issued July 8, 1958, to F. J. Bingley, assigned tothe assignee of the present application, the colored light-emissivestripes are spaced apart and so-called guard stripes are provided in thespaces between the light-emissive stripes. These guard stripes areopaque and non-reflecting. In such a structure the light-emissivestripes are individually defined and impingement of the scanningelectron beam on more than one light-emissive stripe at a time issubstantially prevented. This structure also has other advantages as setforth in said Bingley patent.

In such a structure, the index stripes may be disposed behind the guardstripes so as not to shadow the lightemissive stripes, i.e. so as not toreduce the electron impingement on the light-emissive stripes whichwould debut they may be deposited by "ice grade the color picture.However, a screen structure of this character requires precise alignmentor registry between the index stripes and the guard stripes. Thisimposes a very close tolerance on the manufacture of the screenstructure since any misregistry between the index stripes and the guardstripes would tend to defeat the purpose of having the index stripesbehind the guard stripes.

The principal object of the present invention is to overcome thisdifficulty and to provide an improved screen structure which eliminatesthe necessity of close registry between elements of the structure.

Another object of the invention is to provide a screen structure whichis relatively simple in construction and which permits broadmanufacturing tolerances, and is therefore more economical to construct.

Other objects and features of the invention will be apparent from thedescription to follow. In accordance with this invention the indexstripes are caused to serve both as index elements and as guard stripesbetween the colored light-emissive stripes. The latter stripes aredisposed in contiguous relation to one another, preferably in abuttingrelation, and each index stripe is adjacent to and overlaps portions oftwo consecutive colored light-emissive stripes. The index stripes aremade sufficiently thick so that they are substantially impervious to theelectrons, in order that they may serve as guard stripes in addition toserving as index stripes in the performance of their normal function ofgenerating the index signal.

The invention may be fully understood from the following detaileddescription with reference to the accompanying drawings wherein FIG. 1is a greatly enlarged fragmentary sectional plan view of one form ofcolor image-producing screen structure according to this invention; and

FIG. 2 is a similar view of a modified form of screen structureaccording to the invention.

Referring first to FIG. 1, there is shown a transparent substrate 10which may be the faceplate of a colored image-producing cathode ray tubeor an image plate in proximity to the faceplate. Deposited on saidsubstrate are colored light-emissive stripes in contiguous relation toone another, preferably in abutting relation. Red light-emissive stripesare shown at 11, green light'emissive stripes are shown at 12, and bluelight-emissive stripes are shown at 13. The said stripes preferably aresubstantially equal in width. Since each color triplet represents onecolor cycle of 360 color degrees, each of said stripes may have a widthof color degrees. An electron-permeable light-reflecting layer 14, whichmay be formed of aluminum, is applied to the colored light-emissivestripes. Index stripes 15 are deposited on layer 14 so that each of theindex stripes is adjacent to and overlaps portions of two consecutivecolored light-emissive stripes. By way of example, each index stripe mayhave a width of 50 color degrees and may extend 25 color degrees on eachside of the line of abutment of the two adjacent colored light-emissivestripes. The index stripes are sufficiently thick so that they aresubstantially impervious to electrons, in order that they may also serveas guard stripes.

With this structure there is no requirement of very close registry oralignment between elements. The index stripes could be displaced ineither direction by as much as 25 color degrees before the displacementwould have any noticeable effect.

In this structure the index stripes serve both as index elements and asguard stripes. Thus the guard stripes previously used in spaces betweenthe light-emissive stripes are eliminated and the structure issimplified. Moreover, in this structure the effective width of the col-3,135,891 Patented June 2, 1964 ored light-emissive stripes is notreduced. While the index elements overlie portions of the coloredlight-emissive stripes, such portions thus being rendered ineffective,the effective portions are as wide as are the colored lightemissivestripes in the prior structure having spaces to accommodate guardstripes.

In the screen structure of FIG. 1 there are three index stripes for eachcolor triplet, and therefore the index signal produced by electron beamimpingement of the index stripes has a frequency which is the thirdharmonic of the color writing frequency. However, other indexfrequencies may be produced by modification of the screen structure. Forexample, a 3/2 1 index frequency (f being the color writing frequency)may be produced by causing alternate ones of the stripes to be activeand the other alternate ones to be relatively inactive, although, ofcourse, the inactive stripes will still serve as guard stripes. Thus inFIG. 2, which shows the same screen structure except for thismodification, the alternate stripes 15 are active and the otheralternate stripes 15a are relatively inactive in that they do notcontribute to the index signal. One way of achieving this result is todeposit the stripes 15 and 15a in separate applications, using activatedphosphor for the stripes 15 and inactivated phosphor for the stripes150. Another way is to deposit all of the stripes in one applicationusing activated phosphor, and then apply to the stripes 15a a material,such as aluminum, which is transparent to the electron beam but opaqueto the index phosphor radiation, thus masking stripes 15a from the indexsensing means. Still another way would be to apply to the alternatestripes 15a a material that would poison them in such a way as to reducetheir emission of radiation. Still another way is to deposit all of thestripes in one application using inactive material, and then applyactive material to stripes 15 to render them ,4 active. In any case itis not necessary that the stripes 15a be totally inactive. As long asthey are substantially less active than stripes 15, the latter willproduce a 3/2 f index signal as the electron beam scans across thescreen.

While certain forms of screen structure according to this invention havebeen illustrated and described, it will be understood that the inventionis not limited thereto but contemplates such modifications and otherembodiments as may occur to those skilled in the art.

I claim:

1. An image screen for a color image-producing cathode ray tube,comprising a transparent substrate, parallel. colored light-emissivestripes supported by said substrate in closely adjacent relation to oneanother for transverse scanning by an electron beam, said stripes beingsuccessively and repetitively emissive of light of different colors inresponse to electron beam impingement, an electron permeablelight-reflecting layer on said stripes extending over the entire imagearea of said screen, and relatively narrow electron-impervious stripeson said layer adjacent to and coextensive with the respective facingedges of said light-emissive stripes and overlapping portions of thelatter stripes immediately adjacent the facing edges, at least some ofsaid electron-impervious stripes being constituted to emit energy toproduce an index signal in response to electron beam impingement.

2. An image screen according to claim 1, wherein said coloredlight-emissive stripes are disposed in abutting re lation to oneanother.

References Cited in the file of this patent UNITED STATES PATENTS2,945,087 Graham et al July 12, 1960

1. AN IMAGE SCREEN FOR A COLOR IMAGE-PRODUCING CATHODE RAY TUBE, COMPRISING A TRANSPARENT SUBSTRATE, PARALLEL COLORED LIGHT EMISSIVE STRIPES SUPPORTED BY SAID SUBSTRATE IN CLOSELY ADJACENT RELATION TO ONE ANOTHER FOR TRANSVERSE SCANNING BY AN ELECTRON BEAM, SAID STRIPES BEING SUCCESSIVELY AND REPETITIVELY EMISSIVE OF LIGHT OF DIFFERENT COLORS IN RESPONSE TO ELECTRON BEAM IMPIGEMENT, AN ELECTRONPERMEABLE LIGHT-REFLECTING LAYER ON SAID STRIPES EXTENDING OVER THE ENTIRE IMAGE AREA OF SAID SCREEN, AND RELATIVELY NARROW ELECTRON-IMPERVIOUS STRIPES ON SAID LAYER ADJACENT TO AND COEXTENSIVE WITH THE RESPECTIVE FACING EDGES OF SAID LIGHT-EMISSIVE STRIPES AND OVERLAPPING PORTIONS OF THE LATTER STRIPES IMMEDIATELY ADJACENT THE FACING EDGES, AT LEAST SOME OF SAID ELECTRON-IMPERVIOUS STRIPES BEING CONSTITUTED TO EMIT ENERGY TO PRODUCE AN INDEX SIGNAL IN RESPONSE TO ELECTRON BEAM IMPINGEMENT. 